Storing a 2-dimensional array within a 1-dimensional array

All I'm trying to do here is store a collection within a collection...the collection being arrays. My problem is the syntax. I have built the 2-dimensional array, now I wish to add it to the 1-dimensional array but not sure how to do it. Here is my code below.

    Dim idx As Integer = 0
    Dim arr1() As String
    Dim arr2(,) As String

    Redim Preserve arr1(idx)

    For x As Integer = 0 To 14
         Redim Preserve arr2(x, y)
         For y As Integer = 0 To 9
              Redim Preserve arr2(x, y)
              arr2(x, y) = "Test " & x & " and " & y        
         Next
    Next

    arr1(idx) = arr2

I'm getting an error where I assign arr2 to arr1. It says "Value of type 2-dimensional array of String cannot be converted to String". I also tried this:

    arr1(idx) = arr2()

The above syntax gave me the error "Number of indices is less than the number of dimensions of the indexed array".